libusb: implement zlp flag in libusb transfer
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Authored by aokblast on Aug 6 2025, 12:58 PM.

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Summary

The USB protocol defines a Zero-Length Packet (ZLP) to signal the end of
a transfer when the data size is an exact multiple of the Maximum Packet
Size (MPS). Without a ZLP in such cases, the device may not be able to
determine that the transfer has completed.

This flag is added to libusb to allow the user send a ZLP in the end
of libusb_xfer.

Diff Detail

Repository

rG FreeBSD src repository

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Build Status

Buildable 66339
Build 63222: arc lint + arc unit

Event Timeline

aokblast created this revision.Aug 6 2025, 12:58 PM

Herald added a subscriber: imp. · View Herald TranscriptAug 6 2025, 12:58 PM

aokblast requested review of this revision.Aug 6 2025, 12:58 PM

Harbormaster completed remote builds in B66010: Diff 159849.Aug 6 2025, 12:59 PM

Send packet only the multiple of packet

Harbormaster completed remote builds in B66093: Diff 160029.Aug 8 2025, 7:33 AM

defer zlp check until we can find the xfer

Harbormaster completed remote builds in B66094: Diff 160030.Aug 8 2025, 7:58 AM

lwhsu added a subscriber: lwhsu.Aug 18 2025, 6:18 AM

lwhsu added inline comments.

lib/libusb/libusb10.c
1628	should we use `libusb20_tr_get_max_packet_length()` or `libusb20_tr_get_max_total_length()`?

Get correct MPS

Harbormaster completed remote builds in B66339: Diff 160585.Aug 19 2025, 11:18 AM

This implemented is problematic since the correct way is to append a zero size TRB in TD instead of creating new TD. However, I think I am unable to make it work before 15.0 release. Therefore, I will modify it to at least we won't break any ABI for 15 if we want to merge later.